Visual acuity deficiencies such as myopia (nearsightedness) and hyperopia (farsightedness) are typically corrected with use of refractive lenses such as spectacles or contact lenses. Although these types of lenses are effective in correcting a wearer's eyesight, many wearers consider them inconvenient because they have to be located, worn at certain times, removed periodically and can be lost or misplaced. They can also be dangerous or cumbersome if the wearer participates in sports activities or suffers impact to the eye.
The use of IOLs as a permanent form of refractive correction has been gaining popularity. IOLs have been used for years in aphakic eyes as a replacement for the natural crystalline lens of the eye which has been removed as a result of a cataract. Many different designs have been developed and proved to be successful for IOLs used in aphakic eyes. They primarily include an optic portion and supports, called haptics, connected to and surrounding at least part of the optic portion, for supporting the IOL in the eye in either the anterior or posterior chamber.
IOLs have been made from a variety of biocompatible materials, ranging from the so-called rigid materials such as polymethylmethacrylate (PMMA) to the so-called soft materials that can be folded or compressed such as silicones, certain acrylics, and hydrogels. Haptics have been formed separately from the optic portion and connected through processes such as heat or physical staking and chemical bonding. They have also been formed as an integral part of the optic portion in the so-called single piece IOLS.
Soft IOLs have gained popularity because they can be compressed, folded, rolled or otherwise deformed and inserted through an incision in the cornea that is much smaller than necessary for the rigid lenses which must be inserted through an incision slightly larger than the diameter of the optic portion. When implanted in the eye, these soft lenses then open to their original shape because of the memory characteristics of the soft materials.
When implanted, both soft and rigid IOLs are subject to compressive forces exerted on their outer ends, which typically occur when the individual squints or rubs his or her eye. These compressive forces can result in decentration of the optic and distortion of the visual image because the compressive forces tend to cause translational movement along the optical axis. Movement in this direction could cause the IOL to contact and damage the delicate corneal endothelial layer. Also, because IOLs of current designs, whether formed of soft or rigid materials, tend to deflect along the optical axis when the haptics are compressed, IOL manufacturers have had to provide a range of sizes to fit the IOL to a particular patient's eye to minimize the potential for this movement and thus provide more certain refractive correction.
Because of these shortcomings in IOL designs, there is a need for a haptic design that minimizes translational movement of the optic portion along the optical axis when compressive forces are exerted against the outer ends of the haptics.